This invention relates generally to the field of handling documents and document-handling machines. More specifically, this invention relates to controlling the timing and motion of documents in a document-handling machine, especially that of mailpieces in a mail-handling machine.
The processing and handling of mailpieces and other documents consumes an enormous amount of human and financial resources, particularly if the processing of the mailpieces is done manually. The processing and handling of mailpieces is performed not only by the Postal. Service, but also by each and every business or other site that communicates via the mail delivery system. Various pieces of mail generated by many departments and individuals within a company must be collected, sorted, addressed, and franked as part of the outgoing mail process. Additionally, incoming mail must be collected and sorted efficiently to ensure that addressees receive it in a minimal amount of time. Because much of the documentation and information being conveyed through the mail system is critical to the success of a business, it is imperative that the processing and handling of both the incoming and outgoing mailpieces be performed efficiently and reliably so as not to negatively affect the functioning of the business.
In view of the above, various automated mail-handling machines have been developed for processing mail (i.e., removing individual pieces of mail from a stack and performing subsequent actions on each individual piece of mail). However, in order for these automatic mail-handling machines to be effective, they must process and handle xe2x80x9cmixed mail,xe2x80x9d which means sets of intermixed mailpieces of varying size (from postcards to 9xe2x80x3xc3x9714xe2x80x3 flats), thickness, and weight. In addition, xe2x80x9cmixed mailxe2x80x9d also includes xe2x80x9cstepped mailxe2x80x9d (e.g., an envelope containing an insert which is smaller than the envelope, thereby creating a step in the envelope), tabbed and untabbed mail products, and mailpieces made from different substrates. Thus, the range of types and sizes of mailpieces which must be processed is extremely broad and often requires trade-offs to be made in the design of mixed-mail feeding devices in order to permit effective and reliable processing of a wide variety of mixed mailpieces.
In known mixed-mail handling machines that separate and transport individual pieces of mail away from a stack of mixed mail, the stack of mixed mail is first loaded onto some type of conveying system for subsequent sorting into individual pieces. The stack of mixed mail is advanced as a stack by an external force provided by a stack advance mechanism to, for example, a shingling device. The shingling device applies a force to the lead mailpiece in the stack to initiate the separation of the lead mailpiece from the rest of the stack by shingling it slightly relative to the stack. The shingled mailpieces are then transported downstream to, for example, a separating or singulating device (xe2x80x9csingulatorxe2x80x9d) that completes the separation of the lead mailpiece from the stack so that individual pieces of mail may be transported further downstream for subsequent; processing.
In such a mail-handling machine, the various forces acting on the mailpieces in advancing the stack, shingling the mailpieces, separating the mailpieces, and moving the individual mailpieces downstream often act counterproductively relative to each other. For example, inter-document stack forces exist between each of the mailpieces that are in contact with each other in the stack. These inter-document forces created by the stack advance mechanism, the frictional forces between the documents, and electrostatic forces that may exist between documents, tend to oppose the force required to shear the lead mailpiece from the stack. Additionally, the interaction of the force used to drive the shingled stack toward the singulator and the forces at the singulator can potentially cause a thin mailpiece to be damaged by being buckled as it enters the singulator. Furthermore, in a conventional singulator, there are retard belts and feeder belts that are used to separate the mailpiece from the shingled stack. Both the forces applied by the retard belts and the feeder belts must be sufficient to overcome the inter-document forces previously discussed. However, the friction force generated by the retard belts cannot be, greater than that generated by the feeder belts or the mailpieces will not be effectively separated and fed downstream to the next mail processing device. Moreover, if the feeding force applied to the mailpieces for presenting them to the singulator is too great, xe2x80x9cmulti-feedingxe2x80x9d may occur in which several mailpieces are forced through the singulator without being successfully separated.
Although strong forces seem to be, desirable to accelerate and separate the mailpieces reliably and efficiently, these same strong forces can damage (e.g., buckle) lightweight mailpieces being processed. In response, weak forces may be used to accelerate and separate the mailpieces, but these forces result in poor separation, a lower throughput, and stalling of the mailpieces being processed. The problem is that when both thin mailpieces; which are flimsy and require weak forces to prevent them from being damaged, and thick/heavy mailpieces, which are sturdy and require strong forces for proper separation and feeding, are in the mail stack, stronger stack normal forces may be created due to the thick/heavy mail, requiring stronger nip forces at the singulator; and, these forces may damage the thin mailpieces.
Thus, the apparatus used to separate a stack of mixed mail must take into account the counterproductive nature of the forces acting on the mailpieces and produce an effective force profile acting on the mailpieces throughout their processing cycle to effectively and reliably separate and transport the mailpieces at very high processing speeds (e.g., four mailpieces per second) without physically damaging the mailpieces. However, because the desired force profile acting on a particular mailpiece depends upon the size, thickness, configuration, weight, and substrate of the individual mailpiece being processed, the design of a mixed-mail feeder which can efficiently and reliably process a wide range of different types of mixed mailpieces has been extremely difficult to achieve.
The present invention provides an apparatus and method for transporting documents along a document feed path from an upstream end to a downstream end. The apparatus includes at least one document-handling subassembly along the document feed path for singulating the documents, controlling gaps between the documents, and/or conveying the documents toward the downstream end; a sensor mounted along the document feed path for sensing the positions of the documents and for generating position signals based on the document positions; and a control apparatus for receiving the position signals and for controlling the velocity and acceleration of the document-handling subassembly so as to regulate the size of the document gaps and to maximize document throughput.
Preferably, the document-handling subassembly includes a singulator. The apparatus may also include a second document-handling subassembly such as an input feeder, between the singulator and the upstream end, for feeding documents along the document feed path, a conveyor belt running between the singulator and the downstream end for conveying the documents downstream along the document feed path after the documents leave the singulator, an aligning area downstream from the singulator, through which the documents are bottom-edge aligned as they are conveyed on the conveyor belt, and a third document-handling subassembly such as a second singulator, placed downstream the aligning area, for further singulating the documents as they are transported from the aligning area. Preferably, the sensor transmits signals to coherently control the velocity and acceleration of the input feeder and singulators so as to control the size of the document gaps and maximize document throughput.
Other document-handling subassemblies include a stack advance mechanism at the upstream end for advancing to the input feeder documents from a document stack at the upstream end, a first output feeder between the singulator and the aligning area for taking the documents from the singulator, and a second output feeder between the second singulator and the downstream end for taking the documents from the second singulator to the downstream end.
Preferably, the sensor is aligned with the beginning of the nip area of the singulator. More preferably, there are at least second through eighth sensors placed downstream the sensor, as follows: the second sensor is aligned after the nip of the singulator; the third and fourth sensors are aligned before and after the nip of the first output feeder, respectively; the fifth and sixth sensors are aligned with the aligning area; the seventh sensor is aligned before the nip-of the second singulator; and the eighth sensor is aligned with the nip of the second output feeder.
Preferably, the sensor and the second sensor can sense when a document is clear of the singulator, so as to start the input feeder and singulator operating. The third sensor can sense when a document is in the first output feeder, so as to stop the first output feeder from operating if the stop flag is set. The fourth sensor can sense when a document is clear of the first output feeder, so as to start the singulator operating unless the stop flag is set. The fourth sensor can also sense when a document is in the first output feeder, so as to set the stop flag in conjunction with the fifth and sixth sensors. The fifth and sixth sensors can sense an unacceptably small document gap, so as to set the stop flag. The seventh sensor can sense an acceptable document gap, so as to clear the stop flag and to accelerate the first output feeder after the stop flag is cleared. The eighth sensor can sense when a document is clear of the second output feeder, so as to cause the second singulator to send a second document into the second output feeder.
Preferably, the aligning area also includes a seventh document-handling subassembly, e.g., a trap, for preventing a document from being conveyed along the document feed path when the gap between the document and a downstream document is unacceptably small and the first output feeder is unable to stop the document.
The apparatus of the present invention can operate at accelerations as low as 0.5 g, enabling documents to be transported with constant motion through the apparatus, thereby maintaining efficient inter-document gaps without using high accelerations.
Additional advantages of the invention will be set forth in the description which follows, and in part Will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.